Various triazine-based herbicides have heretofore been known. For example, 2-methylthio-4,6-bis(alkylamino)-s-triazine derivatives are known to be effective herbicides having a high weed control activity. However, the effect of 2-methylthio-4,6-bis(ethylamino)-s-triazine, for example, greatly varies with conditions such as the type of soil and temperature. In more detail, when used in a mild district, it causes phytotoxicity (chemical damages) even in the commonly used amount, and in a cold district, its effect is exhibited only insufficiently. Thus 2-methylthio-4,6-bis(ethylamino)-s-triazine has a disadvantage in that it can be applied as a herbicide only in a limited district.
Under such circumstances, paddy herbicides prepared by the substitution of the alkylamino group of 2-chloro-4,6-bis(alkylamino)-s-triazine or 2-alkylthio-4,6-bis(alkylamino)-s-triazine derivatives with an .alpha.,.alpha.-dimethylbenzylamino group have been proposed (see, for example, Japanese Patent Publication Nos. 8261/74 and 8262/74). These compounds do not cause phytotoxicity to paddy rice plants and have herbicidal activity against annual weeds, but their effect against perennial weeds causing problems at present is undesirably low.
The present invention is intended to overcome the above problems and an object of the present invention is to provide a process for preparing a novel herbicide which can exhibit a nearly equal herbicidal effect under various soil and temperature conditions or irrespctive of the type of soil and temperature, does not cause phytotoxicity, and can effectively kill various weeds from annual to perennial weeds.
As a result of extensive investigations, it has been found that the above object can be attained by using specific triazine derivatives.